Radio broadcasting system



De@ 15 1942 L c. ROBERTS l y 2,305,496

RADIO BROADCASTING SYSTEM Filed Aug.y 28, 1941 A 2 sheets-sheet 1 27 I I l f? M I T 1 /6\.` Am? Aw'o. l 70 TUM- Auro. l I FIL. kc I Muay/vc: FIL 4 ccrs. l

| f 24 25 76 77 zoi/ V26 74 l v 7a l 79 Wm smr/o/v /va/ FIL We TRANS. d f/g A T TORNE V RADIO BROADCASTING SYSTEM v Filed Aug. 28, 1941 2 Sheets-Sheet 2 Flc. 4"

AHORA/Ey Patented Dec. 15, 1942 RADIO BROAD CASTING SYS TEM Leland C. Roberts, Towaco, N. J., assi'gnor to Bell Telephone Laboratories, Incorporated, New York, N'. Y., a corporation of New York Application August 28, 1941, Serial No. 408,615

8 Claims.

This invention relates to a radio broadcasting system, and more particularly to arrangements for automatically broadcasting the call lettersy of individual stations embodied in such system, in response to a signal originating at a control station.

Heretofore, stations comprising a broadcasting system disconnected themselves individually from the system in response to an announcement, Vsuch as This is the XYZ broadcasting system," given usually from the control point at which thev common program originated; Thereafter, an attendant at the individual stations proceeded to give an oral announcementof theA identifying'call letters. the movements of the attendants preclude all stations from simultaneously effecting the call letter broadcast, it may happen thataportion of `the-time allotted to the common program is consumed in the call letter broadcast. Such lost time may bev more or less, depending on whether the station identification is given at quarter-hour or' halfhour intervals. Consequently,y a system embody'- ing a relatively large number of stations may1 be called upon to reserve as much as one minute for the time differential in broadcasting its individual station call letters in order that the common program will not run over its allotted time. Such time differential isfwasteso far as commercial utility is concerned.

This invention contemplates an arrangement to effectautomatically in a broadcasting system the simultaneous. announcement of the call letters of the individual stations comprising such system, in response to a signal originating at a control station.

The main object of the invention is to minimize the time diiferential between the broadcast of individual station identifications in a multi-sta-A tion radio system.

Another object is to effect substantially simultaneously the broadcast of the call letters of all stations embodied in a broadcasting system.

A further object is to operate on an unattended basis the individual stations embodied in a broadcasting system.

In the specific embodiment, the invention comprises a control station supply a common program to a plurality of individual broadcasting stations connected therewith by a suitable transmission line, each broadcasting station embodying a transmitter and antenna. Normally, the control station is effectively connected to the inasmuch as various factors including station. When it is desired to send out the cali letters' of all broadcasting stations in the. system, a suitable signal produced at the control station is applied to the connecting transmission line. This signal is simultaneously utilized at all'broadcasting stations to disconnect said latter stations from the transmission line and simultaneously therewith to operate an announcer device which applies the call letter energy4 to the transmitter and antenna embodied in the individual broadcasting stations. After the cail letter energy has been broadcast each announcer device functions to disconnect itself from the transmitter andA antenna and at thesame time to-y reconnect 'efn fectively the individual broadcasting stations to the transmission line to receive the common program.

A feature of the invention is thatthe call letter broadcast of the several stations of a radio system Another feature ensures that' the call' letter broadcast takes place substantially simultaneously at all such stations. A further feature relates to minimizing the time differential between the broadcast of the call letters of several individual stations connected together in a radio transmission system. Another featureenables a relatively close check of the timeallotted for the broadcast'of a common program among the several individual stations operating in such system.

Another feature involves the elimination .of attendants at individual broadcasting stations.

The invention will be readily' understood from the following description taken together with the accompanying drawings in which:

Fig. l is a schematic circuit diagram illustrating a radio broadcasting system including two embodiments of. the invention;

Fig. 2 is a schematic circuit diagram showing one embodiment of the invention;

Fig'. 3 is a partial schematic circuit diagram taken along the lines 3--3 of each of Figs. 2 and is effected on an automatic basis.v

contacts I1, I1 of a normally unoperated electro-` magnetic relay IS to a radio transmitter I9 and associated antenna 28, both of which essentially constitute the broadcast station I3 whose circuit arrangement and operation will now be described.

In the line I6 at a point intermediate the contacts I1, I1 and the line I2 may be disposed a suitable amplifier 2|. Across the line I3 at a point intermediate the contacts I1, I1 and the transmitter I9 are connected in sequence a filter 24, an amplifier-rectier 25, and an automatic announcer apparatus 26 which is also connected to the relay I8 and a pair of open contacts 21, 21 associated therewith.

Referring to Fig. 2, which shows in detail the circuit portion of Fig. 1 below the line X--X,

the apparatus 26 in the station I3 of Fig. l

comprises a normally unoperated electromagnetic relay 23 whose open contact 29 is applied to a ground 38 and whose armature 3I extends over a lead 32 and winding of electromagnetic relay 33 to the positive terminal of a source 34 of direct potentialwhose negative terminal is grounded. To the Winding of the relay 33 is connected a lead 31 which extends to one brush terminal of a direct current motor 38 whose'other brush terminal is connected to the positive terminal of a source 39 of direct potential whose negative terminal is grounded. i To vthe lead 31 is connected a lead 40 whic extends through the winding of the relay. I8 to the positive terminal of a source 4I of direct potential whose negative terminal is grounded. Also, connected to the lead 31 is a normally open contact 42 of the relay 33 whose associated armature 43 is extended over lead 44 to normally closed contact 45 to which is connected ground potential 46, both of which are associated with electromagnetic relay 41.

A reproducing device U is the familiar telegraphone type comprising an endless band of magnetic material applied onto pulleys B5 and 66 of which the latter pulley has its shaft 52 connected by an endless belt 53 to the armature 54 of the motor 38. Pick-up magnet 55 positioned in proximity of the reproducing device 50 serves to apply call letter information recorded thereon l over a 4line 56 embodying a suitable amplifier 51 to the normally'open-contacts 21, 21 associated with the relay I8. The call letter information of the reproducing device 58 includes the call letters of the station I3 whose identity is to be lbroadcast in a manner that will be subsequently explained.

Ground 58 is applied to armature 49 of relay 33 and may be extended over open contact 59, lead 60, pair of contacts 6I, 6I and conducting surface 62, Fig. 3, affixed suitably to the reproducing device 50, when the latter is in the proper position as will be later explained, lead 63, winding of relay 41 to the positive terminal of a source 64 of direct potential whose negative terminal is grounded. In connection with Fig. 3, the conducting surface B2 is so aiiixed to the reproducing device 50, Fig. 3, as to complete the electrical circuit between the contacts 6 I, 6I once for each complete revolution of the reproducing device 58 in order to effect certain action which will be hereinafter pointed out.

In the operation of Figs. 1 and 2 when it is desired to broadcast call letters to identify station I3, a preselected signal, such as a 100G-cycle wave modulated with a -cycle wave, is supplied by the source II to the lines I2 and IS. Disregarding station I4 for the moment and as contacts I1, I1 are closed due to the normally unoperated condition of relay I8, this preselected signal is selected from the line I6 by the filter 24, amplied and rectied in the amplifier-rectifier 25, and thereafter impressed on the winding of relay 23. The rectified signal operates relay 23 to supply ground potential 38 over a circuit comprising contact 29 closed on armature 3I of relay 28, leads 32 and 48, winding of relay I8 to the direct current source 4I. Relay I8 operates to open the contacts I1, I1 thereby disconnecting the transmitter I9 from the line I2. This terminates signaling transmission from the source II. At the same time the operation of relay I8 closes contacts 21, 21 to connect the line 55 and pick-up magnet 55 to the transmitter I9 and associated antenna 20.

Also, at the same time ground potential is supplied over a circuit comprising Contact 29 closed on armature 3l of relay 28, leads 32 and 31, and motor 33 to the direct current source 39; and relay 33 is caused to operate due to anenergizing circuit comprising ground potential 30, contact 29 closed on armature 3| of relay 28, lead 32, winding of relay 33 and the direct current source 34. Relay 33 locks up in a circuit comprising direct current source 34, both the winding and contact 42 closed on armature 43 of relay 33, lead 44, and closed contact and ground potential 46 of relay 41. Also relay I8 is locked up in a circuit comprising source 4I, winding of relay I8, lead 40, contact 42 closed on armature 43 of relay 33, lead 44 and closed contact 45 and ground potential 4S of relay 41. The operation and lock-up of relay 33 serves to close the armature 58 on the contact 59 thereby applying ground potential 58 over lead 60 to one of the contacts 6I, 6I for a purpose which will be mentioned later.

As the motor 38 is now energized in the manner previously described, the pulleys 65 and 66 are rotated to pass the reproducing device 50 before the pick-up magnet 55 for the reason that the energizing circuit for the motor 38 is locked up inI a circuit comprising direct current source 39, motor 38, lead 31, contact 42 closed on armature 43 of operated relay 33, lead 44, and contact 45 and ground potential 46 of relay 41. The call letter energy picked up by the magnet 55 from the reproducing device is Vapplied over line 56, amplifier 51, closed contacts 21, 21 of relay I8, line I6 to the transmitter I9 to be broadcast on the antenna 28 associated therewith.

A sufficient length of blank space is provided on the reproducing device 50 at the start of its rotation so as to enable the motor 38 to come up to such speed as is proper to venable a relatively high quality broadcast of the call letter energy picked up from the reproducing device 5D. To control the speed of the motor 38 a suitable governor may be embodied therein. After the reproducing device 59 has made one complete'r'evolution, the contacts El, 5I complete via the conducting surface 62, Figs. 2 and 3, a circuit comprising ground 58, armature 49 closed on the Contact 53 of operated relay 33, lead 60,

by lan endlessy belt 95 to a shaft of'a. pulleyv contacts 6I, `6| and conducting surface 62 (Figs. 2 and 3), lead, Winding` of relay 41 and the positiveV terminal ofthe direct potential source This circuit Winding of the relay Q1 which operates to open the contact 45 to interrupt the previously traced holding/circuit of the motor 38 thereby stopping the movement of the reproducing device 58. At this point it is tor be noted that the relay 28 is released at the conclusion of the signal 1oeing sent from-the central station Iii. Also, the previously traced holding circuitsv for the relays I8 and 33 are interrupted. The release of relay AI8 closes the contacts I1, I1 to reconnect the line i2 to the transmitter I9 of the broadcast station I3. The release of relay 33 :further interrupts the hereinbefore defined lock-up circuits for the motor 38 and relay I3. The control of the operation of the motor 38 is such that the abovementioned blank portion of the recording device i) is always stopped before the pick-up 'magnet 55. The release of relay 33 also interrupts the previously described engagement between the armature 49 and contact 59 to remove the ground potential 53 from one of the contacts 6|, /6I thereby interrupting'at this point the hereinbefore mentioned energizing circuit for the relay t1. The contacts 6|, 6| are spaced relative to each other, on the conducting surface 62, Fig. 3,

such that the inertia of the motor 38 causes the interruption of the energizing circuit of relay i1 at this point before the reproducing device 50 returns to a state of rest.

5I, 6| are out of engagement with the conducting surface |52 as shown in Fig. 3. The automatic announcer apparatus 2t is now conditioned for the succeeding appropriate signal to effect a subsequent broadcast of the call letters of the stationIS.

Referring again to Fig. l a transmission line 'i0 connects the transmission line I2 through a pair of closed contacts 1I, 1| of a normally unoperated electromagnetic relay 12 to a radio transmitter 13 and associated antenna 14, both of which essentially constitute the broadcast station Id Whose circuit arrangement and operation will now be explained. In the line 18 at a pointintermediate the contacts 1|, 1| and the line I2 may be disposed a suitable ampliiier 15. Across the line it at a point intermediate the contacts 1|, 1| and the transmitter 13 are connected in sequence a filter 16, amplifier 11, selectively tuned circuits 13 and an automatic announcer apparatus 19 which latter apparatus is also connected -to the relay 12 and open contacts 88, 88 associated with the latter.

Referring now to Fig. 4 which shows in detail the circuit portion below the line Y-Y of' causes an energization of the.

|62V on which and another pulley I|l3 is mounted a reproducingdevice of the telegraphone type aforementioned with respect to the reproducing device 58. Pick-up magnets' 99 isV connected 'by Y line |65) and amplifier IUI to the normally open With the reproducing device 5i) in tlie'latter state, the contacts Fig. l, the output of the amplifier 11 is applied n across the selectively tuned circuits 1S. The

latter comprise essentialiy series tuned circuits Sd, 85 and 83 arranged in parallel and connected across the input of a triode amplifier 81, normally biased by resistor 83 near its cut-off, by slow-release electromagnetic relays 89 and 99 disposed in the output thereof.

Announcer apparatus 19 connected by a lead S3 to the tuned circuits 18 is substantially identical with the announcer apparatus 26 thereinbefore described in connection With the station i3 and shown in Fig. 2. Accordingly, announcer apparatus 19 embodies essentially a direct current motor 93 whose armature 94 is connected contacts 88, of relay 12.

In the operation of Figs. 1 and 4, when it is desired to broadcast call letters to identify station le a preselected signal, such as the successively familiar three tones having frequencies fi, f2 and f3, is applied by the source II to the lines I2 and le. Disregarding station I3 for the moment and as the contacts 1|, 1| of relay 12 are closed, this preselected signal is selected from the line 1E] by the filter 16, ampliiiedv in amplifier 11 and thereafter impressed on the three tuned circuits 84, 85 and 86 which are individually resonant at the respective frequencies fI, f2 and f3.

The tone 'fI selected by the tuned circuit 84 producesa control voltage across inductance II!) embodied therein. This voltage is impressed on the control grid of the amplifier 81 in a circuit comprising ground potential I||,iinductance IIU, lead H2, normally lclosed contact II3 of relay 89, control grid and cathode of amplifier 81, biasing resistor 88 and ground potential H4. As the amplifier Was initially biased substantially at cuto, this control Voltage renders the control grid of the amplifier 81 less negative by an amount which is suiiicient to occasion a flow of anode current in a circuit comprising positive terminal of source IIS of direct potential Whose negative terminal is grounded, Winding of relay 89, lead IIS, normally closed contact |09 of relay 88, anode and cathode of amplifier 81, biasing resistor' 88 and ground potential H4. The iosvv of anode current in such. circuit serves to operate the relay 8&1.`

The tone f2 selected by the tuned circuit 85 produces a control voltage across inductance I I1 embodied therein. This voltage is impressed on the control grid of amplifier 81 in a circuit comprising ground potentialr I I8, inductance I I1, lead IIS, normally closed contact |20 of relay 9B, lead |2I, closed contact |22 of operated relay 89, control grid and cathode of amplifier S1, biasing resistor 88 and ground potential IM. As the amplier 81'Was initially biased near cut-off, this control voltage renders the control grid of the amplifier 81 less negative by an amount which is adequate to cause a oW of anode current in a circuit comprising ypositive terminal of a source |23 direct potential Whose negative terminal is grounded, winding of relay 90, lead |24, normally closed contact |25 of relay 9i), lead |25, closed contact |21 of operated relay 89, anode and cathode of amplifier 81, biasing resistor S8 and ground potential I i4. The iioW of anode current vin such circuit'serves to operate the relay 9S.

The tone f3 selected by the tuned circuit Sii produces a control voltage across inductance t28 included therein. This voltage is impressed on thecontrol grid of theamplier 81 in a circuit lcomprising ground potential |29, inductance |28, lead |39, closed Contact |3| of operated relay 9i), lead IZi, 'closed contact |22 of operated relay 89, control grid and cathode of amplifier 81, biasing resistor` 88, and ground potential |I4. As'the amplifier 81 Was initially biased near cut-ofithis initial voltage renders the control gridv of the amplifier 81 less negative by an amount which is adequate to occasion av ovv'ofranode current in a circuit comprising positive terminal of source |32 'of direct potential Whose' negative terminal is grounded, normally closed contact I 35 of relay 92, lead |33, Winding of relay 9|, lead 93, closed contact |34` of operated relay 90, lead |26, closed Contact |21 of operated relay 89, anode and cathode of amplifier 81, biasing resistor 88 ,and ground potential I4. The flow of anode current in such circuit serves to operate the relay 9| which locks up in a circuit comprising source |32, closed con tact |35 ofrelay 92, lead |33, Winding of relay 9|, resistor |46, closed contact |43 of operated relay 9| and ground potential |44. Due to a slow-release feature, both relays 89 and 99 remain operated until'the 'relay 9| is operated in the afcrementionedV manner.

The operation of relay 9| completes for the relay 12 an energizing circuit comprising positive terminal of source |40 of direct potential Whose negative terminal is grounded, Winding of relay 12', lead 4|, lead |42, closed contact |43 of operated relay 9| and ground potential |44. Relay 12 operates to open contacts 1|, 1| and to close contacts 80, 80. At the same time, the operation of relay 9| completes for the motor 93 an energizing circuit comprising positive terminal of source |45 of direct potential Whose negative terminal is grounded, brushes of motor 93, lead |46` lead |41, lead |42, closed contact |43 of operated relay 9| and ground potential |44. Motor 93 operates to drive the pulley |02 which passes the recording device 98 before the pick-up magnet 99. The call letter energy picked up thereby is applied over line |00, amplifier closed contacts 80, 89 of operated relay 12, line 10 to the transmitter 13 and associated antenna 14 shown in Fig. l.

After the recording device 98 has made one entire revolution, the contacts 6|, 6| complete via the conducting surface 62, Figs. 3 and 4, a circuit comprising source |48 of direct potential WhoseV the hereinbeiore described energizing circuits for the relay 12 and motor 93. Release of the relay 12 closes the contacts 1 1| to reconnect the line to the line !2 and at the same time to open the contacts 89, 89. Deenergization of the motor 93 serves to stop the movement of the recording device 98 before the pick-up magnet 99. 'Ihis therefore terminates a broadcast of the call letter energy supplied by the recording device 98.

The operation of the motor 93, recording device 98 and pick-up magnet 99 embodied in the announcer apparatus 19 of Fig. 4 is substantially identical with the operation of the corresponding elements embodied in the announcer apparatus 26 of Fig. 2 to eiiect a high quality broadcast of the call letter information. After the relays 12, 99, 90, 9|, and 92, and motor 93 are returned to their unoperated condition, the circuit arrangement shown in Fig. 4 is conditioned to receive the succeeding three tones fl, f2 and f3 to effect a subsequent broadcast of the call letters of station |4.

While Fig. 1 shows broadcasting stations |3 and |4 equipped With call letter announcing ap- This occasions an energization of the Windpurpose of facilitating this description, and in practice the broadcasting stations whose call letters are to be automatically announced simultaneously in response to signals originating in a central station should be equipped so as to respond to the same signal. This would mean that all individual broadcasting' stations embodied in the one radio system are equipped with identical v call letter announcer apparatus such as that shown in either Fig. 2 or Fig. 4.

Itis to be understood that While the reproducing device supplies the call letter energy to identify individual stations; such device could also be utilized to supply advertising or other information of a purely local character. Hence, such information could be broadcast locally without interfering with the broadcast of the common program.

What is claimed is:

1. In combination in a transmission system, a source of intelligence signals including a preselected signal, a plurality of intelligence signal transmitting stations spaced from said source, each of said stations embodying broadcasting means, circuit means to connect said source with said stations'such that normally said intelligence signals are eiectively applied to said broadcasting means, and means at individual stations to respond to said preselected signal such that said broadcasting means are disconnected from said source for a certain time interval during which otherl signals are effectively applied to said broadcasting means.

2. A radio broadcasting system comprising a control station, a plurality of broadcasting stations each of Which includes an antenna, circuit means to connect effectively said control station with said broadcasting stations. such that normally said control station is connected to said antennas, means at said control station to apply a preselected signal to said circuit means, and means at individual broadcasting stations to respond to said preselected signal such that said antennas are disconnected from said circuit means for a certain time interval during which call letter signals are caused to be applied eifectively to said antennas of said broadcasting stations.

3. A radio broacasting system comprising a control station, a plurality of broadcasting stations each of which includes an antenna, circuit means to connect said control station with said broadcasting stations such that normally said control station is effectively applied to said antennas, means at individual broadcasting stations to disconnect said control station from said circuit means and to apply call letter signals to said antennas associated with said individual broadcasting stations and after a certain time interval to reconnect said individual broadcasting stations to said circuit means, and means at said control station to apply a preselected signal to said circuit means to actuate said disconnecting and reconnecting means at said individual broadcasting stations.

4. A radio broadcastingsystem comprising a control station, a plurality of broadcasting stations, each of which includes an antenna, a transmission line to connect said control and broadcasting stations such that normally said control station is effectively connected to said antennas, means at individual broadcasting stations to produce a call letter signal, means at individual broadcasting stations to disconnect said latter stations from said line and to connect effectively said call letter producing means to said antennas associated With said latter stations such that substantially simultaneously with such connec-tion said call letter producing means are rendered operative and after a certain time interval said call letter producing means are rendered inoperative and substantially simultaneouslir therewith are disconnected from said antennas and said individual broadcasting stations are reconnected to said line, and means at said con-trol stati-on to apply a preselected ksignal to said line to actuate substantially simultaneously said disconnecting and reconnecting means at said individual broadcasting stations.

5. In combination in a signal transmission system, a source of intelligence and preselected signals, at least one intelligence signal transmitting station, circuit means to connect said source and said station such that normally both said source and station are eiective to transmit the intelligence signals, and means at said station to respond to the preselected signal such that both said source and station are rendered ineffective to transmit the intelligence signals for a cer-tain time interval and said station is rendered effective, during the certain time interval, to transmit -other signals to identify said station.

6. A signal transmission system comprising a plurality of stations to transmit common signals at the same time,` and means at individual stations to disable said stations substantially at the same time for transmitting the common signals for a predetermined time interval and to cause the individual stations substantially simultaneously to transmit other signals duringthe predetermined time interval.

7. A radio broadcastingy system comprising a plurality of -signal transmitting'stations, a central station for intelligence and preselected signals, circuit means to connect said central station to said transmitting stations so that said latter stations normally transmit the intelligence signals substantially at the same time, and means at individual signal transmitting stations controlled by the preselected signal to render said central station and said signal transmitting stations ineiective substantially at the same time to transmit the intelligence signals for a predetermined time interval and to enable the individual signal transmitting stations substantially simultaneously to transmit other signals during the predetermined time interval.

8. A radio broadcasting system comprising a plurality of stations each including an antenna, a source of intelligence and preselected signals, circuit means Yto connect said source to said stations such that normally said source is effectively connected to said antennas for transmitting the intelligence signals substantially at the same time, and means at individual stations controlled by the preselected signal to render both said source and stations ineffective substantially simultaneously to transmit the intelligence signals for a predetermined time interval and to cause said stations substantially at the same time to transmit other signals during the predetermined time interval.

LELAND C. ROBERTS. 

